overcurrent protection for canadian code.

Discussion in 'Homework Help' started by peeka, Aug 30, 2009.

  1. peeka

    Thread Starter Member

    Apr 25, 2009
    21
    0
    following 3 phase continous duty service motor are connected to a common copper feeder.
    28 amp FLC full voltage start squirel cage motor
    72 amp FLC full voltage start squirel cage motor
    130 amp FLC full voltage same as above

    what is the maimum rating of non time delay fuse that would b permitted as overcurrent protection for the feeder... answer = 450.

    now ive been trying on this for AGES , i jsut cant get my head around where the hell i go to find this information i get crazy answers....one is 130 X 2 (table 29) then add the sum of other motors, which = 360. but then wat ? the circuit breakers table 13 wont match 450 n i could use 400....so i dont know im stuk.....
     
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    Rule 28-204(1) states that you start with the highest drawing motor and calculate it's over current device according to rule 28-200, which calls upon table 29.

    In your example the 130 amp motor requires a NTD fuse rated at 390. Table 13 lists a 350 fuse, as the next higher value exceeds.

    Rule 28-204(1) further states that you add the amperages of the remaining motors. So for your example; 350 + 72 + 28 = 450. You again go to table 13 to determine the closest device that does not exceed this value.

    Now that we've figured that out, what's the minimum size of that feeder conductor?
     
    Last edited: Sep 1, 2009
  3. peeka

    Thread Starter Member

    Apr 25, 2009
    21
    0
    u explain it so easily lol :p thanx alot dude appreciate ur help well my exam is tomoro so just going thru final things from the exambank questions , coz its all codebook only a few calculations i had last time so yea . well thanx :)
     
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    if it's your 3rd year electrical, as I recall, the exam has about 20% code related question. Make sure you know your phase angles.
     
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